Manufacture of carboxylic acids



1 rai niea petize 1941 ref-pm NT'f orFl'cE MANUFACTURE or omnoxrmc Acni's "John F. 01m, GrosseIIeQandFr-ederick'P.Fritsch, Wyandotte, Mich, and George Hinds, Phila-f *delphia, Pa., assignors to' Sharples Oh Inc., acorporation of Delaware micals- Nonravving. Application Ma 13, 1939',

l 7, Serial No.213482 12- Claims. (Cl. 260531)-- =1 The present invention relates tothe manuiacture' of carboxylic acids. Anpbjectof theinvention haslbeen t'o'provide 'a processwhereby,

aliphatic carboxylic acids can be producedby an economical procedure, from raw materials 1 which are readily availablein large quantities.

It is Well known that primary alcohols may be corresponding ketone,"' 'and that this ketone is oxidizedto produce acids. When pantanol-l, for

example, is oxidized, valeric acid may be obtained together with other oxidation products, and

when prirnary iso-a'myl alcohol is oxidized, isovalericacid isproduced among the oxidation products. M q .1 The oxidationof a tertiaryalcohol is extreme- 1y difficult, and when'it is effected, ketones and acids are obtained,; but theacids so formed are usually oxidized further. with the result that the bulk of thealcohol is converted into carbon di- V i 1 A secondary alcohol cannot be converted into an acid, by simpleoxidatiomand such"oxidatlon,

therefore, results in the production. of 'ketones without forming any acid. An object of the pres-r ent invention has been to provide a processor.

oxidizing secondaryalcohols and ketones to pro- 7 duce carboxylic acids. Sincejsecondary alcohols can beproduced in large quantities bythe simple hydration. of olefins derivedfrom petroleum or other sources, the useoffthis, plentiful and economical source 'of raw material for the prepara--- tion of carboxylic acidsafiordslahighly desirable process.

or ketones to undergo a series'of reactions 111-,

f eluding scission of the'aliphatic hydrocarbon radical at the point of attachment of the hydroxyl radical, or, ketone oxygen" thereto, and an oxidation at the point of scissiontoproducetwo molecules of carboxylic acid' from the secondary, alcohol or ketonemolecule. The alcohol or ketone molecule thus'jlundergoes a combined splitting and oxidation, reaction.

Vario pionlc,j ',butyric, Valerie, caproic, caprylic, capric," etc., andmixtureslof these various acids can be 'carboxylic acids, such as acetic, profrom suchi'scissio n.

nisrn or the reactions obtained'inlthe practice of the invention, it. is beli'evedthat the results ob- 'tainedmaybe explained on the, basis that the secondary alcohol is firstfoxidized to produce the then split 'and oxidizedfto produce acetic acid and 'propionic acid simultaneously "by oxidation of the compoundsprradicals resulting from the splitting operation; ifl thistheoryiscorrect, the I reactions involved ma lowing eguations;

e illustratedby the fol- While theinventlon "maybe secondary alcohols and ketones, containing from i v 3 to -'20 carbon atoms, for example, it will be described (ior'the sake'of simplicity of explanation), in connectlon wlth the conditions of temperature, acid concentration, method of puritying the crude reaction mixture, and other details, found tobe "most suitable for the manufacture of alcohols by" performance or combined splitting and oxidation reactions on'such alcohols (or' ketones) containing between 3 and 8 carbon atoms. Since the application of the prinproduced by the technique or theinvention.

Thusfwhen 3 -hydroxy normal pentane is oxidized by means of nitric acid in the practice or the invention, amlxture' is obtainedcontaining acetic acid and propionic acid, by scission o! the. alcohol molecule at the hydroxyl radical and oxidation oithe compounds or radicals resulting with the understanding that similar treatment Zmaybe applied to the manufacture of similar ciples of the-invention to the'splittingand oxidation of ketones involves a procedure which is identical to that involved in the treatment of secondary alcohols, except with respect to time of reaction, theinvention' willlbedescribed in its application to the oxidation ofsecondary alcohols containing between 3 'and'8 carbon atoms,

acids from ketones of corresponding carbon content, as 'well as from the corresponding alkyl sulfates; In the treatment or secondary alcohols a 'whilefiveidonotl sh limitedfoah speciiic'theoryLas to the mechapracticed to effect simultaneous oxidation andsplitting of various in the practice of the invention, the combined splitting and oxidizing reaction referred to above may be accomplished by treatment of the alcohol with nitric acid having a concentration between and 70%. The reaction may be accomplished at temperatures-between 23 and65",=' 0., although temperatures toward the upper of this range are preferred. Reaction temperatures which are much higher than 65 C. are undesirable in the treatment of lower secondary alcohols, since a part ofthe alcohol is lost by" distillation in case .higher temperatures are employed. The best yields from-the practice of the concentration between and is employed. The remainder of the secondary alcohol is next gradually added to the reaction mixture, and the mixture is stirred and artificially cooled during the addition of this remaining alcohol, in order to maintain the reaction mixture within the temprature limits discussed above. Care should be invention have been obtained in connection withoperations in which the reactionztemperature.

was maintained between flfi. and 55 C. during the major part of the course of the reaction.

When very dilute nitric acid is used, higher tem-' peratures should be employed in order to speed up the reaction, and when relatively strong nitric acid ..(e.,' g. between 55 and"70% concentration) is used, the temperatures should ordinarily be lie- 1 low "C, inorder'to avoid reaction of such violence as might resultin anexplosion, and unoontrollable oxidation to produce undesired highly n15 preferredthat the quail-my of n fitric acid in casesdn'which them o1. .ratiobfjnitric acid to secondary alcohol was at la-stas high as 2:1.

The very best yields 'so'cfar obtained in the practice of theinvention'have been obtained in cases 7 used, in the vpracticef of theprocess'be in con- 1 .siderable molecular excess of the total quantity ors condarye c no1 treated andlbestresults in thepract'iceofitheinventionhave been obtained taken to.avoid adding the alcohol so rapidly as to build up a high concentration of alcohol, with subsequent rapid reaction causing a rise of temperature substantially above the limits above indicated, since rapid rise of temperature causes too rapid reaction with, danger of explosion, and

promotion of undesired side reactions to produce highly oxidized products.

add the secondary alcohol, while avoiding undue "temperature rise, has varied between 1 and 5 hours in'experiments conducted in the practice of the invention, depending upon operating conditions.

After all of the alcohol to be oxidized has been passed into' the reactor, stirring of the reaction mixture is continued (usually for a period between 15 and 50 minutes), until the splitting and 'oXidation reaction'ito produce the desired acids has been completed, as indicated by the fact that no more gasis evolved.

T After the reaction'i's completed, the reaction mixture isdiluted to precipitate from solution products'of side reactions which are insoluble in water, such as aldehydes; ketones and esters. The aqueous solution so obtained, contains the in which the mol. ratio. of nitric acid to second-' ary alcohol was approximately 3:1.

In :the' practice of the invention, best results are'obtained by first reacting a small amount of the secondary alcohol (or ketone) with the nitric acid, to effect splitting and oxidation, with formation of oxides of nitrogen as by-produc-ts',

and thereafter gradually adding the remainder of the'secondary alcohol (or .ketone) to be treated.- The products of oxidation obtained by the initialtreatment of a small amount of the secondary alcohol with the nitric acid seem to have an auto catalytic effect in promoting the reg action, and best results in the practice, of the invention have been, therefore, obtained in cases in which reaction iS first accomplished to proing a small amount of the secondaryyalcohol to i the acid in the reactor. In connection with this is accompanied by the evolution of brown fumes gen. When the evolution of such fumesincon- Vnection with the small amount of. secondary alcohol initially added, has ceased, the oxidation of the main bulk of the secondary alcohol to be treated may be commenced.

. operation-oxidation takes-place promptly, and

- resultingfrom the formation .of oxides of nitro- 1.

desired carboxylic acids and nitric'acid. In order tosepar'ate unreacted nitric acid. from the carboxylic acids, the aqueoussolution of this mixture of acids is extracted with a solvent which selectively dissolves the c'arboxylic,v acids while leaving the nitric acid in aqueous solution. Care should be taken in the choice of the selective solvent. to be used for this purpose, to avoid use of a, solvent, which will, itsel f, be oxidized by the nitric acid. The'various aliphatic'ethers, such asdi-ethyl ether, di-propyl ether, di-butyl ether, and particularly 'dl-iso-pr'opyl ether, have been [found to be excellent solvents for effecting this selective extraction .of'the carboxylic acids from the nitric acid solution- Gases evolved during the course of the reaction are passed, together with air, through a scrubber system, whichmaybe a system for counter-currently extracting the oxides of nitrogen by treatment with water. Such a treatment has the advantage that it effects regeneration of nitric acid; and this, nitric acid may be used in the subsequent practice of the process on another batch of alcohol; The use o'f acid derived from the scrubbing systemin this way has the advantage that such acid containsa small quantity of the by-products of reaction and of incompletely oxidized material. The return of acid containing su'ch materialhas twoadvantages. In the first place, the return ofinadequately oxidized alcohols or ketones enables these materials to be subjected to treatmentin a subsequent batch for In the oxidation of the main bulk of the sec ondary alcohol, after oxidation of a small quantity of such alcohol has been acornplished, as described.above the'mixture of nitric acid and re- I when products in the reactor is first cooled to a temperature between 2 3' and 65? C., preferably between 45 and 55 C., when nitric acid having a adequate oxidation. and thus'improves the yield. In the second place, the return of by-products of reaction, which are not, desired in connection with the oxidationofa further batch'of secondary alcohol, depresses the formation of s milar compounds in the treatment of thissecond batch, in accordance with the principles of the law of mass action. The solution of nitric acid obtained by selective extraction of the organic acids from the reaction mixture, by means of isopropyl ether, for example, may Slmila m an Ma to The time required to by ad ion of-water tothe 'reaction mixture.

, ;tt8,15 108,ll1 the practice oftheprocess. In cases acid employedginthe reaction is reduced to nitrogen, and thisundesiredareductionis not avoided ratios of 1 acid to alcohol are employed.-

After considerable experimentation, the app'li-V n riee du el t esen m e minimized f byincorporating in.theureaction mixture a comp ndehes f om: t e l ssp lst s of m .wHQUliQqiOXidB, :ar timony tri-chloride, stannous T l 4 chloride,;cohalt nitrateqand nitrates of mercury.

a-qThese compounds areeflective to inhibit reductnscli g tte .px lj i r'in s agdescribed above. a certain amountoi nitric acid is reduced -nitrogen, andjthereduction of the oxides offnitrogento elemental-l nitrogen represents a;

;,inwh ich}di ethyl carbinol split and oxidized in thepracticefof the; invention, it frequently thappens that between fand of the nitric) 2,267,377 or itreatni'en the next batchi 3 Example 2.--By adding 10 g. SnCla to the hot HNO: along with-2 cc. of alcohol and proceeding as above, theamount oi BNO: reduced to nitroon tlie supernatant. aqueous acid phase formed :1 V

(gen decreased to 20% with approximately the same yield of alcohol to acid.

Examplede-When 3 molaof methyl ethyl car:

hlnol ise'c. hutyl alcohol) was "oxidized by theuse of 10 mols. of HNO: as in Example 1. 1.72 mols,

of acetic acid and 0.6'niol. oi propionic acid were obtainedto givelan alcohol yieldoi 38.6% to the acids. 7

Example 4.-.-3 mols. or pentanol-2 were reacted I with 'l2'mo1s. of nitric acid at a temperature of even in cases in whichextrernely high molecular "C.,after init iating the reaction by adding a Iveryismall quantity or pentanol-2 to the nitric acid at a temperature between 90 and 95 C. as described in Examplel, 'Thetechnique followed in this'operation wasfotherwis'e identical as that cants hayediscovered.that the reduction of the).

tiomto produce .nitrogen regardless-oi the propor i ns" in wh hl..theyearein o po a ed ey ware etlecti-ve as ,reductioninhibitors when incorporated in proportions even as small as 0.1%,fa'nd thelr efiect is therefore,gobviously a catalytic .DQ mfQImtHZQDQ 11 as efiective as higher-con}- centratiomdn mos ,ases

he completes charge of alcohol e nit ic a d, wate y b tion minture' immediately upon :ors-anim c daam zdilu le" nitric acid. nd asuper; atant: cilznhasecont n ns other p odu e hewcompletionofrthe Oxidation reaction, has the cuts. in the. {case at such prompt water dilution. In case thewater is added promptly and'extracable.-tc..retumctheaoihphase stratifled iromthe aqueous phase...to the; -next.batch oi material to bezztneatedesmcethis o'ihphase' contains a con;

l coiildib'fir'iaintained and the excessive evolution of "gas avolded'."j1% hours wererequired' for :ona- 'lhe estla esultshaye been. obtained ininlstancesdnvwhich; these; reduction inhibitors are l employed in ratios varying between 0.3 and 5%,

1 cruise; c ncentration-oi.appro imately 0.3%. has '35 1. Y a I carbon atom (these mayhecdnsideredias carboxy alteinatiyegctogthecontinuation of the, j t

thebcmhpletionr ct"- the-addition of the secondary ohcliiand'.the-.mixture.mayathcn vbe promptly hstcatifiedt into:tan aqueous phase containing the advantage:thatv the reaction mixture'can be more Vasily an.d jefiectivelm separatedinto 'its constit- I tion promptly effected, ,itwlll, of course, be desir n 2 cc.) of di ethyl carbinol was f "stan as oxidation-started. the mass was cooled to (SO-65 C. and the alcohol (3 mols.)

,was heaters: a rate at which the temperature of propionic acid. and 0.62

."oi hutyric acid wereformed A conversion 61568.57}, of the alcohol to acids Wasthus obtained.

Further modifications willibe'ohyious' to those Yskilledin the artand j we'do not. therefore, wish to bel'liinited except bythe s cpeQtthe'suhjomea claims. ,When secondary alcoholsa'iie referred to in the'se clam itgis tcihe understood that this 1 .the simple monohyd' wndaryalcoholsl diice'Q-hydroxy stearic acid, and may thereafter be oxldiz'cdQbjr.

expression isnotj interpreted as-limited to tached'to an jinternal carbonotan aliphatic hydroXylradIcal is attached t ql'a. non-terminal the invention, oleic acid may ,stearic acid nitric acid in accordance with "thefinyention, to I produce, from onemoleculefoi Q-hydrdxy stearic dditicn;of.1.:watenpromptly. w t u wa s V l p p p joined claims to. treatment of af'secondary alco- 1 5 isiderable proportion l'oi'cinadequately oxidized. ma

acid a molecule or mono-car'hoxylic 9-carbon ato'rn acid' and a molecule ofidi-carboxylic 9- carbon atom acid. and such procedure is intended to be included, when'reierence is made in the subprocess comprising reacting secondary oxy comand the sulfuric acid esters of secondary alcohols with nitric acidfto split the alkylfr'adical of said compound and oxidize said compound to produce two-moleculesof..carboxyliclacid'irom a single temperature substantially in excess'oi '70 C., and

v reacting said added compound with the nitric acid, thereafter cooling the reaction mixture to a molecule i or said compo nd, h n. reaction being. accomplished by tlrstfi'nixing fa very small proportion 7 of said compouniwith nitric acid at a temperature below C., and adding the rema'iningquantity of said compound to be reacted with said nitric acid to} said reaction mixture gradually while cooling the reaction mixture to maintain it at a temperature below 65 C. during the reaction of the remaining alcohol with the nitric acid to complete'the formation of carboxylic acids.

2. In the process of manufacturing carboxylic acids by oxidation with nitric acid of an open chain type oxy compound selected from the class consisting of ketones and secondary alcohols, the

I 'secon'darylalcohols, since the expressionds usedjitoTdesignate the broad I class of compounds having ahydroxylradical at- .lli rated to pro- 1. In the manuiactureof carhonylic acids, the

improvements that comprise heating together initially a small quantity vof the compound with the 3. In the process of manufacturing carboxylic acids by oxidation with nitric acid of an open chain type oxy compound selected from the class consisting of ketones and secondary alcohols, the improvements that comprise reacting initially at a temperatu ,-"above 70 C. a small quantity of the compouii "with the acid and thereafter completing the oxidation by adding and reacting within the temperature range 23 to 65 0. further quantities of 'the'compound to the acid at'a rate substantially equal to the rate of oxidationof the compound to carboxylic acids.

4. In the process of manufacturing carboxylic acids by oxidation with nitric acid of an open chain type oxy compound selected from the class consisting of ketones and secondary alcohols, the improvements that comprise reacting initially within the temperature range 90 to 95C. a small'quantity of the compound with the acid and thereafter completing the oxidation by adding and reacting within the temperature range a temperature below 65 C., the concentration of the nitric acid used bing about 50% based on 7 weight.

9; Inthe process of manufacturing carboxylic acids by oxidation withjnitric acid of an open chain type oxy compound selected from the class consisting of ketones and secondary alcohols, the improvements that comprise addingthe compound in small incremental quantities to 5 the nitric acid while maintaininl the acid initially 23 to 65C; further quantities of the compound to theacid at a rate substantially equal to the rate of oxidation of the compound ,to carboxylic acids.

5; In the "process of manufacturing carboxylic acids by oxidation with nitric acid of an open chain type oxy compound selected from the class consisting of ketones and secondary alcohols, the

improvements that comprise reacting initially within the temperature range 90 to 95 C. a small quantity of the compound with the acid and thereafter completing the oxidation by adding and reacting within the temperature range to C. further quantities of the compound to the acid 6. In the process of manufacturing carboxylie I,

acids by. oxidation with nitric acid of an open chain type 'oxy compound selected from the class consisting of ketones and secondary alcohols, the improvements that comprise adding the com pound in small incremental quantities to the nitric acid while maintaining the acid initially at a temperature above 70 C. and thereafter at a temperature below 65 C.

7 In the process of manufacturing 'carboxylic acids by oxidation with nitric acid of an open chain type oxy compound selected from the class consisting of ketones and secondary alcohols, the improvements that comprise adding the com pound in small incremental quantities to the.

nitric acid while maintaining the acid initially at a temperature above 70 C. and thereafter at a temperature within the range 23 to 65 C.

8. In th process of manufacturing carboxylic acids by oxidation with nitric acid of an open chain type oxy compound selected from the class at a temperature above 70 C. and thereafter at a temperature within the range 23 to 65 C., concentration of the nitric acid used being about 50% based on weight.

10. In the process of manufacturing carboxylic acids by oxidation with nitric acidof an open chain type oxy compound selected from the class consisting of ketones and secondary alcohols, the improvements that comprise heating together indtially fa small quantity of the compound with the acid until substantially reacted and thereafter completing the oxidation by adding further quantities of the compound to the acid at a rate substantially equal to the rate of oxidation of the compound to carboxylic acids, the concentration of the nitric acid used being about 50% based on weight, while maintaining the temperature of the reaction mixture substantially constant.

11. In the process of manufacturing carboxylic acids by oxidation with nitric acid of an open chain type oxy compound selected from the class consisting of ketones and secondary alcohols, the improvements that comprise heating together initially a small quantity of the compound with the acid until'substantially reacted and thereafter completingithe oxidation by'adding further quantities of the compound to the acid at a rate substantially equal to the rate of oxidation of the compoundto carboxylic acids, the reactions ,being performed at substantially cons-tantrtemconsisting of ketones and secondary alcohols. the

improvements that comprise adding the compound in small incremental quantities to the -nitric acid while maintaining the acid initially at a temperature above 70 C. and thereafter at a temperature below C., the reactions being performed in the presence of catalytic quantities of a substance selected from the class con-,

JOHN F. OLIN. FREDERICK P. FRITSCH. GEORGE E. HINDS. 

